Negative battery main contactor status determination

ABSTRACT

A system, method, and battery control module for detecting negative contactor status of a battery, such as a high voltage vehicle battery, is disclosed. The method includes applying a constant current to a bipolar transistor element having a base, an emitter, and a collector, wherein the base is electrically connected to a first resistor and an analog-to-digital converter, the collector being electrically connected to a second resistor and a diode. A collected current is delivered by the collector, and the method includes injecting the collected current through the second resistor and the diode and into a negative contactor of a battery. The method also includes determining a resistance across the negative contactor of the battery. The system may include a battery having a negative contactor, the negative contactor having a switch side, and a battery control module in communication with the battery.

TECHNICAL FIELD

The present disclosure relates to hybrid and electric vehicle systems,and more particularly, to battery management systems for high voltagebatteries.

BACKGROUND

Government regulations and consumer desires demand that vehiclescontinuously improve on fuel economy and emissions. At the same time,vehicle affordability is a concern, in light of the numerous automotiverequirements and increasing costs. Accordingly, there is a need for morefuel efficient and low-emission engines that are also without addedcomplexity and cost.

Electrically powered and hybrid (conventionally fossil fuel power incombination with electrical power) vehicles are a viable solution forreducing emissions and improving fuel economy. Such vehicles arebecoming increasingly attractive alternatives to fossil fuel poweredcars. Electric and hybrid vehicles require high voltage applicationshaving relatively large capacity battery systems with relatively largeamounts of power compared to a 12 V automobile storage batter. However,because of the high voltage requirements, significant safety concernsare raised.

Accordingly, high voltage battery management systems incorporate safetyfeatures and monitoring systems. For example, negative contactors of thehigh voltage battery packs are monitored to determine whether thenegative contactor is open, closed, or in-between, in order to determinewhether the high voltage battery pack can be safely connected and usedwithin the vehicle.

Conventional high voltage battery management systems typically performhigh voltage (HV) level control from the low voltage (LV) side of theboard. That requires the HV sensors, actuators, and communication to beisolated from, and transported to, the LV side of the board by way ofoptical photomos or digital isolators. Such systems typically use asignificant number, e.g., 14, isolation components between the highvoltage side and the low voltage side of the board. Components of thistype are expensive, and automotive qualified components of this type arelimited.

Various methods have been used for contactor negative status detection.In one example, switching components, such as a photomos, may be usedand controlled from the low voltage side of the board. The midpoint ofthe pack may be used as a main reference to all other voltagemeasurements and ground for active components. Voltages more negativethan the midpoint, like the contactor negative, then require anoperational amplifier as an active component, to invert the signal andallow the use of a positive voltage analog-to-digital converter (ADC).This results in an analog voltage measurement, from which, with detailedsystem knowledge, the resistance of the negative contactor can bedetermined. Due to interference with changing high voltage packpotential, however, as well as needed circuitry, this solution isexpensive and may be inaccurate.

In another example, the voltage drop created by the load current throughthe negative contactor may be measured, resulting in a measurement ofthe contact resistance of the contactor. A load current is required, andat low load currents, a voltage drop is difficult to measure due to thelow contact resistance of the contactor.

In yet another example, a voltage may be injected, and the effect of theDC link on the voltage may be measured to determine the contactorstatus. This method, however, may not be accurate, and more componentsmay be needed to protect for higher voltage, as the voltage sourced usedfor injection is typically the HV Battery Pack itself.

Accordingly, a need exists for a simple solution to determine thenegative contactor status, which is cost effective.

SUMMARY

Disclosed is a system, method, and battery control module for detectingcontactor negative status in a high voltage battery system, which issimple, cost effective, and without added complexity or additionalhardware components.

In one form, which may be combined with or separate from the other formsdescribed herein, a method for detecting negative contactor status of abattery is disclosed. The method includes applying a constant current toa bipolar transistor element having a base, an emitter, and a collector,wherein the base is electrically connected to a first resistor and ananalog-to-digital converter, the collector being electrically connectedto a second resistor in series with a diode, the collector delivering acollected current. The method further includes injecting the collectedcurrent through the diode and into a negative contactor of a battery,and determining a resistance across the negative contactor of thebattery.

In another form, which may be combined with or separate from the otherforms disclosed herein, a system for detecting negative contactor statusof a battery is disclosed. The system includes a battery having anegative contactor, and the negative contactor has a switch side. Abattery control module is in communication with the battery. The batterycontrol module includes a diode and a first resistor, the first resistorand the diode being electrically connected with the negative contactor,and a bipolar transistor having a base, an emitter, and a collector, thecollector being electrically connected to the first resistor. Thebattery control module also includes a second resistor and ananalog-to-digital converter, each of the second resistor and theanalog-to-digital converter being connected to the base of the bipolartransistor. A constant current source is electrically connected to theemitter of the bipolar transistor. The battery control module isconfigured to apply a constant current through the constant currentsource and to determine a switch side resistance of the negativecontactor.

In still another form, which may be combined with or separate from theother forms described herein, a battery control module configured todetermine negative contactor status of a battery is provided. Thebattery control module includes a first control logic configured toapply a constant current to a bipolar transistor element having a base,an emitter, and a collector, the base being electrically connected to afirst resistor and an analog-to-digital converter. The collector iselectrically connected to a second resistor and a diode, the collectordelivering a collected current. A second control logic is configured toinject the collected current through the second resistor and the diodeand into a negative contactor of a battery. A third control logic isconfigured to determine a resistance across the negative contactor ofthe battery.

Further features and advantages of the present disclosure will becomeapparent from consideration of the following description and theappended claims, when taken in connection with the accompanyingdrawings. It should be understood that the description and specificexamples are intended for purposes of illustration only and are notintended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples are reflected in the drawings, which will be described below.The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.The drawings show:

FIG. 1 is a schematic circuit diagram illustrating a system fordetecting for negative contactor status of a battery, included in abattery control module, in accordance with the principles of the presentdisclosure; and

FIG. 2 is a block diagram illustrating a method for detecting negativecontactor status of a battery, according to the principles of thepresent disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Certain terms are used throughout the following description and claimsto refer to particular system components and configurations. As oneskilled in the art will appreciate, companies may refer to a componentby different names This document does not intend to distinguish betweencomponents that differ in name but not function. In the followingdiscussion and in the claims, the terms “including” and “comprising” areused in an open-ended fashion, and thus should be interpreted to mean“including, but not limited to . . . ”.

Examples of the invention are described below. It should be noted thatthese and other examples or embodiments are exemplary and are intendedto be illustrative of the invention rather than limiting. While theinvention is widely applicable to different types of systems, it isimpossible to include all of the possible embodiments and contexts ofthe invention in this disclosure. Upon reading this disclosure, manyalternative embodiments of the present invention will be apparent topersons of ordinary skill in the art. Other embodiments may be utilized,and other changes may be made, without departing from the spirit orscope of the subject matter presented here.

With reference to FIG. 1, a system for detecting negative contactorstatus of a battery is illustrated and generally designated at 10. Thesystem 10 includes a battery 12 having a HV switching element on itsnegative pole, typically in form of a contactor 14, as illustrated inFIG. 1. The battery 12 may be a high voltage battery 12, for example,having a voltage in the range of about 150 V to about 400 V. The battery12 may also have an unknown parasitic resistance 15 in parallel with thenegative contactor 14. The negative contactor 14 may be the high voltagevehicle DC Link, having a nominal zero voltage and transients of, e.g.,−600V to +600V.

A battery control module 16 is in communication with the terminals ofthe battery 12. The battery control module 16 includes an isolatedvoltage source 18 connected to circuitry which creates a current source20 having a voltage drop 22 across the current source 20. The currentsource 20 is electrically connected to a bipolar transistor 24, such asa bipolar junction transistor. The bipolar transistor 24 has an emitter26, a base 28, and a collector 30. The current source 20 is electricallyconnected to the emitter 26.

A resistor 32 is electrically connected to the collector 30, a diode 34is electrically connected to the resistor 32, and the diode 34 iselectrically connected to the negative contactor 14 HV switchingelement, inside the battery 12. Each of the collector 30, the resistor32, the diode 34, and the negative contactor 14 are connected in seriessuch that the resistor 32 is disposed in series between the collector 30and the diode 34, and the diode 34 is disposed in series between theresistor 32 and the negative contactor 14; or in another variation, thediode 34 may be disposed in series between the collector 30 and theresistor 32, and the resistor 32 may be disposed in series between thediode 34 and the negative contactor 14. Another resistor 36 and ananalog-to-digital converter (ADC) 38 are electrically connected to thebase 28.

The battery control module 16 is configured to apply a constant currentthrough the constant current source 20 and to determine a switch sideresistance of the negative contactor 14.

A high voltage/low voltage barrier is schematically illustrated at 40.The high voltage/low voltage barrier 40 has a high voltage side 42 and alow voltage side 44. The high voltage side 42 is partitioned from a setof low voltage functions on the low voltage side 44 to minimize thecommunication that occurs between the high voltage side 42 and the lowvoltage side 44 of the board. A logic controller 46 on the low voltageside 44 may communicate with the battery control module 16 on the highvoltage side 42 via one or more dedicated serial communication buses 48,such as CAN, SPI, or the like. As shown, the battery control module 16is configured to control the switching element of the battery 12 fromthe high voltage side 42 of the high voltage/low voltage barrier 40.

The battery control module 16 is configured to determine the resistanceacross the negative contactor 14 of the battery 12 by referencing to ahigh voltage ground 50. The battery control module 16 is configured tomeasure with the analog-to-digital converter (ADC) 38 and transmit ananalog-to-digital converter measurement across the high voltage/lowvoltage barrier 40 via the serial protocol 48.

The isolated power supply 18 has to have a higher voltage than the sumof the max voltage through the ADC 38 plus the voltage through thetransistor 24 plus the voltage drop 22. However, the power supply 18does not need to be a well-regulated power supply. The current source 20can be built using components specified for low voltages. The constantcurrent can be chosen with respect to the expected resistance range tobe measured and the maximum acceptable power losses on the bipolartransistor 24, during maximum negative transient voltage on the vehicleDC Link.

The known current will divide between the base 28 and the collector 30of the bipolar transistor 24. Operating the bipolar transistor 24 insaturation most of the time, a drift in its current amplification, doesnot cause any error in the measurement. By measuring the base 28current, the collector 30 current, and therefore contact resistance ofthe negative contactor 14 can be determined.

The resistor 36 is used as a sense resistor, to translate base 28current to a voltage, which can then be converted by the ADC 38. Theresistor 36 is selected with respect to the ADC 38 range and thegenerated constant current. By choosing a bipolar junction transistor 24that can withstand the difference of the maximum negative transientvoltage on the DC Link from the voltage generated by the isolated powersupply 18 (V_18—maximum negative transient voltage on the DC Link), thecomplete circuit is protected from negative transients. By choosing adiode 34 that can withstand the difference of the maximum positivetransient voltage on the DC Link from the voltage generated by theisolated power supply 18 (V_18—maximum positive transient voltage on theDC Link), in reverse direction, the complete circuit is protected frompositive transients.

A constant current is beneficial over known solutions where the currentsource 20 is replaced by a resistive element, due to better accuracy andcomparably simple implementation of measures to protect from transientvoltages on the DC Link. A comparably lower voltage is required to beblocked by the transistor 24, during negative voltage transients on theDC Link. In a 400V battery pack, for example, the transistor 24 could bebiased to 1 kV, which limits available components significantly.

Thus, the battery control module 16 may be configured to determinenegative contactor status of a battery by implementing certain controllogics. For example, the battery control module 16 may have a firstcontrol logic configured to apply a constant current to the bipolartransistor element 24, a second control logic configured to inject thecollected current through the resistor 32 and the diode 34 and into anegative contactor 14 of a battery 12, and a third control logicconfigured to determine a resistance across the negative contactor 14 ofthe battery 12. The battery control module 16 may be configured todetermine the resistance across the negative contactor 14 of the battery12 by referencing a high voltage ground 50. The second control logic maybe configured to inject the collected current into a DC Link side of thenegative contactor 14 of the battery 12. The battery control module 16may be configured to measure with the analog-to-digital converter 38 andtransmit an analog-to-digital converter measurement across the highvoltage/low voltage barrier 40 via a serial protocol 46, by way ofexample.

Referring now to FIG. 2, a method for detecting negative contactorstatus of a battery is illustrated and generally designated at 100. Themethod 100 may be used with the system 10 illustrated in FIG. 1, ifdesired. The method 100 may include a step 102 of applying a constantcurrent to a bipolar transistor element having a base, an emitter, and acollector, the base being electrically connected to a first resistor andan analog-to-digital converter, the collector being electricallyconnected to a second resistor in series with a diode.

The method 100 may also include a step 104 of injecting the collectedcurrent through the diode and into a negative contactor of a battery,and a step 106 of determining a resistance across the negative contactorof the battery. The steps 102, 104, 106 may incorporate other steps asdescribed anywhere herein, such as described above. For example, theinjecting step 104 may include injecting the collected current into a DCLink side of the negative contactor of the battery. The method 100 mayalso include a step of controlling the switching element from a highvoltage side of a high voltage/low voltage barrier. The step 106 ofdetermining the resistance across the negative contactor of the batterymay include referencing a high voltage ground. Further, the method 100may include powering the current source with an isolated power supply.The method 100 may include measuring with the analog-to-digitalconverter and transmitting an analog-to-digital converter measurementacross a high voltage/low voltage barrier via a serial protocol.

It is further understood that any of the above described concepts can beused alone or in combination with any or all of the other abovedescribed concepts. As a person skilled in the art will readilyappreciate, the above description is meant as one illustration of theprinciples of the invention. This description is not intended to limitthe scope or application of the invention in that the invention issusceptible to modification, variation, and change, without departingfrom the spirit and scope of the invention, as defined in the followingclaims.

What is claimed is:
 1. A method for detecting negative contactor statusof a battery, the method comprising: applying a constant current to abipolar transistor element having a base, an emitter, and a collector,the collector being electrically connected to a first resistor in serieswith a diode, the collector delivering a collected current, the basebeing electrically connected to a second resistor and ananalog-to-digital converter; injecting the collected current through thediode and into a negative contactor of a battery; and determining aresistance across the negative contactor of the battery.
 2. The methodof claim 1, wherein the step of injecting the collected current throughthe first resistor and the diode and into the negative contactor of thebattery includes injecting the collected current into a DC Link side ofthe negative contactor of the battery.
 3. The method of claim 2, thebattery comprising a switching element, the method further comprisingcontrolling the switching element from a high voltage side of a highvoltage/low voltage barrier.
 4. The method of claim 3, wherein the stepof determining the resistance across the negative contactor of thebattery includes referencing a high voltage ground.
 5. The method ofclaim 4, further comprising powering the current source with an isolatedpower supply.
 6. The method of claim 5, further comprising measuringwith the analog-to-digital converter and transmitting ananalog-to-digital converter measurement across a high voltage/lowvoltage barrier via a serial protocol.
 7. A battery control moduleconfigured to determine negative contactor status of a battery, thebattery control module comprising: a first control logic configured toapply a constant current to a bipolar transistor element having a base,an emitter, and a collector, the collector being electrically connectedto a first resistor and a diode, the collector delivering a collectedcurrent, the base being electrically connected to a second resistor andan analog-to-digital converter; a second control logic configured toinject the collected current through the first resistor and the diodeand into a negative contactor of a battery; and a third control logicconfigured to determine a resistance across the negative contactor ofthe battery.
 8. The battery control module of claim 7, wherein thesecond control logic is configured to inject the collected current intoa DC Link side of the negative contactor of the battery.
 9. The batterycontrol module of claim 8, wherein the collector, the first resistor,the diode, and the negative contactor are connected in series, the firstresistor being disposed in series between the collector and the diode,the diode being disposed in series between the first resistor and thenegative contactor.
 10. The battery control module of claim 9, thebattery comprising a switching element, the battery control elementbeing configured to control the switching element from a high voltageside of a high voltage/low voltage barrier.
 11. The battery controlmodule of claim 10, the battery control module being configured todetermine the resistance across the negative contactor of the battery byreferencing a high voltage ground.
 12. The battery control module ofclaim 11, further comprising a current source powered by an isolatedpower supply.
 13. The battery control module of claim 12, the batterycontrol module being configured to measure with the analog-to-digitalconverter and transmit an analog-to-digital converter measurement acrossthe high voltage/low voltage barrier.